Ride sharing of any type comes into existence in situations where a significant additional incentive is provided by the market as a reward for sharing. Ride sharing (of any kind) occurs in the following scenarios: 1. Communities where inhibitions are low enough, and promotion active enough, that a small but sufficient proportion of ‘right minded’ individuals can organise to habitually ride share. 2. Car pool (HOV) lanes where travel time can be significantly reduced by ride sharing. 3. Destinations where parking is at a premium and ride sharers are given priority as a result of some policy decision. 4. Scenarios where sufficient sponsorship is available to encourage ride sharing, as a result of some social responsibility or green agenda perhaps.

We might also expect new ride sharing opportunities to appear where: 5. Congestion charging or road pricing schemes where charges can be shared. 6. Fuel prices escalate to such an extent that cost avoided by ride sharing is sufficient to motivation when shared by the passenger and driver. 7. [others]

By way of example, a previous dynamic ridesharing [reference: project] justified the costs of running the system and providing free parking spaces with the value of the parking spaces saved (which might be equated to the revenue from additional train-riders, since parking is a significant constraint on ridership). In fact, while the scheme failed the authority for the particular BART station authority have since built a 1500-space parking garage at a cost of $28,000 per space. Straight-line amortization over 15 years says that's $1,867 per year, or more than $7/day over 250 workdays per year. Most parking spaces go for $1/day at that station; monthly reserved parking spaces (less than 20% of the total) go for $3/day. Therefore, spaces emptied by sharing represent a net value of $6/day or $4/day that could be saved and paid to incentivise the rider and pay for the system.

In principle, vehicle occupancy rates should be higher than the current levels. Ride sharing should play a larger role in the mix of transport modes, because of the external benefits (pollution, land use, congestion). However, the structure of the transport system currently, is such that the incentives required to enable ride sharing are not available, or under-priced.

Inhibitor: sufficient incentives exist (say $2 per trip) that could be harnessed to encourage ride sharing are difficult to find, other than in very niche scenarios.

Inibitor: dynamic ride sharing may only break beyond niche scenarios when the cost of motoring increases dramatically. This macro trend is clear, there is some risk associated with the timing.